This invention relates to a booster charge explosive for transferring detonation from one explosive system to an adjoining explosive system.
It is highly desirable in the oil and gas industry to perforate or make a number of holes in a well bore casing and in the adjacent hydrocarbon bearing geological formation. A common method is to lower into a well bore, a wireline or a tubing perforation gun assembly that includes a large number of shaped explosive charges maintained in certain positions perpendicular to the axis of the well bore. If the hydrocarbon bearing formations are longer than a typical perforation gun assembly, then it is necessary to join or "tandem" additional guns together in order to perforate the entire production geological formation.
In the use of more than one perforation gun assembly, it is necessary to join the guns together so that means are provided to initiate detonation of the successive gun. Generally throughout the industry the detonation means includes a pair of boosters. The first booster located at the bottom of the first perforation gun, is called a "donor" because it passes detonation onto the next successive gun. The second booster located at the top of the next gun is called the "acceptor" because it receives the detonation from the "donor" and initiates the discharge of the shaped charges of the next perforation gun.
Currently, the law prohibits the transportation or storage of charged well perforation guns with boosters attached, because of the potential safety hazard of an accidental detonation. As a result of this law, the guns must be assembled and armed for use in the uncontrolled environment of the site. The attaching of the boosters in this environment greatly increases the safety risks at the site and incidence of gun failures in the well bore.
This problem has been addressed specifically by Regalbuto, U.S. Pat. No. 4,850,438. The Regalbuto patent discloses a modular perforation gun that employs only secondary explosives for the shaped charges, the detonating cord and the acceptor and donor boosters. The use of secondary explosives minimizes the chance of accidental initiation by fire, electrical or frictional spark, or impact. Generally, if set afire these explosives would most often burn out nonviolently. But the booster pellet at the top of the cord and the charge at the cord bottom are both covered by cover plates to provide a dustproof, water-resistant chamber. This sealing of the secondary explosives makes the booster more volatile, and therefore capable of detonating to their full potential and thereby accidentally discharging the shaped charges of the perforation gun.
An alternative solution to this problem is an explosive safe arming apparatus for perforation guns shown by DerMott, U.S. Pat. No. 4,319,526. The DerMott patent disclosed a system for wireline perforation guns having an enclosed carrier with an access port therein, an explosive means in the carrier, which includes at least one shaped explosive charge, a receptor detonating explosive cooperatively arranged and adapted for detonating the shaped explosive charge, and a donor detonating explosive adapted for detonating the receptor explosive. The donor detonating explosive included two encased elements, the first element being fixedly secured within the carrier, and the second element being removably mounted within the carrier and adapted to be inserted into the carrier through the access port into an operative relationship with the first element and the receptor detonating explosive. This second element must be disposed through the access port of the carrier into a retention means to arm the perforation gun and the explosive safe arming system. The DerMott patent provided a means for safer arming of perforation guns, but still requires that the arming of the perforation gun be made under possibly severe environmental conditions, which could contribute to a malfunction or an unsafe or improper operation.